1. Technical Field
The present invention relates to a semiconductor device, and to a technique applicable to, for example, a semiconductor device including a vertical transistor.
2. Related Art
A semiconductor device is known to have a vertical transistor. The vertical transistor is used in, for example, an element that controls a large current. The vertical transistor is known to have a trench gate structure. As the vertical transistor having a trench gate structure, there is a technique disclosed in, for example, Specification of U.S. Pat. No. 7,323,386. In Specification of U.S. Pat. No. 7,323,386, the transistor has a structure in which an N layer and a P layer serving as a base are formed on an N+ layer serving as a drain, and an N+ layer serving as a source is further formed on a surface layer of the P layer. A gate electrode having a trench structure stretches from the P layer toward the N layer. The lower end of the gate electrode gains entrance to the N layer.
In Specification of U.S. Pat. No. 7,323,386, a P shield layer is formed in the lower portion of a trench, instead of the gate electrode. An insulating film is formed between the gate electrode and the P shield layer, and a sidewall insulating film is formed between the P shield layer and the N layer. Further, Specification of U.S. Pat. No. 7,323,386 discloses that the P shield layer and the sidewall insulating film are formed within a separate trench from a gate, and the P shield layer is connected to a source electrode.
A low on-resistance and a high withstanding voltage against a drain voltage are required for the vertical transistor. However, generally, a decrease in on-resistance and an increase in withstanding voltage are in a trade-off relationship, and thus are not likely to be made compatible with each other at a high level.
Other problems and novel features will be made clearer from the description and the accompanying drawings of the present specification.